Heat-pump apparatus for providing heat for domestic and like purposes



Nov. 18, 1958 M. w. R. CAPPS ET AL 2,850,493

HEAT-PUMP APPARATUS FOR PROVIDING HEAT FOR DOMESTIC AND .LIKE PURPOSES 4 Sheets-Sheet 1 Filed June 2, 1952 Nov. 18, 1958 M w. R. cAPPs ET AL 2,860,493

HEAT-PUMP ARPARATUS FOR PROVIDING HEAT FOR DOMESTIC AND LIKE PURPOSES Filed June 2, 1952 4 Sheets-Sheet 2 nu mm ,1958 M w R. CAPPS ET AL 2,860,493

HEAT-PUMP AI PAR ATUS FOR PROVIDING HEAT FOR I DOMESTIC AND LIKE PURPOSES Filed June 2, 1952 Y 4 Sheets-Sheet 3 FIG. 4

66 5 FIG. 7 57:

ven/ars 7 W 11/. 7- um M dz/ Nov. 18, 1958 HEAT-PUMP ARPARATUS FOR PROVIDING I'IEAT FOR Filed June 2. 1952 M w. R. cAPPs ETAL 2,860,493

IO C 65 hive/17ers um; runny/ 0 mm d/w United States Patent HEAT-PUMP APPARATUS FOR PROVIDING HEAT FOR DOMESTIC AND LIKE PURPOSES Martin William Richard Capps, Nina Constance Capps,

and Arthur William Francis Capps,'Edgcumbe, Crowthorne, England Application June 2, 1952, Serial No. 291,214

Claims priority, application Great Britain June 4, 1951 4 Claims. (Cl. 62-238) This invention relates to apparatus operating on the heat-pump principle for providing heat for domestic, industrial, agricultural, horticultural and the like purposes.

By performing mechanical work low-grade heat, extracted from a relatively cold body or source, can be converted together with the heat equivalent of most of the mechanical energy expended, into high-grade heat and transferred to a relatively hot body or sink.

If the supply of mechanical power for operating the heat-pump is continuous and substantially constant, and the temperature of the cold source does not vary within wide limits, the heat output and the temperature range over which the heat can be abstracted for utilisation is substantially constant; but if the power supply is intermittent of fluctuates widely, or if the temperature'of the cold source varies within wide limits, the problem of heat-storage becomes important. This is especially so in domestic installations in which the heat-demand fiuctuates seasonally, substantially in anti-phase with the temperature of any natural, easily available cold source, such as the soil, river or standing water or the atmosphere. a

Our invention is devised to meet these conditions and also to make use of natural sources of power, especially the wind, which introduces the condition of intermittence and fluctuation of input-power in an aggravated form. It is of course to be understood that in its broadest aspect the invention is not limited to installations using windpower.

With a view to simplicity and independence of supplies of expensive materials we prefer to use water and its vapour as the working substance or fluid of'a cycle'of the evaporative and condensing type; and the atmosphere is preferably used as the primary heat source, it being understood that, in the present context, atmospheric heat is deemed to include heat derived directly from solar radiation, when available.

Considered from one aspect, an apparatus according to our invention, operating on an evaporative and condensing cycle with water and its vapour as the working fluid and with sub-atmospheric pressures throughout the cycle, comprises an evaporator in heat-exchange relation with the atmosphere, a compressor and at least two heataccumulating devices for extracting heat from and thereby cooling and condensing the compressed working fluid, namely a high-temperature heat-accumulator in nonmixing heat-exchange relation with the working fiuid discharged from the compressor, and a low-temperature heat-accumulating device constituted by a tank containing a large body of water in heat-exchange relation with the working fluid after it has parted with some of its heat to the high-temperature heat-accumulator, the said tank being buried in the ground, whereby the surrounding soil constitutes a further heat-accumulator.

According to a further feature of the invention, the apparatus may include pipes of porous material, but capable of sustaining a partial internal vacuum, buried in the ground in the neighbourhoodof the buried tank,-

together with valve means enabling the suction side of the compressor to be connected to said pipes, the pipe system being closed except for such connection, whereby heat accumulated in the soil can be utilised for evaporating water supplied to the pipes by percolation from the surrounding soil or otherwise, when the ambient temperature is too low for eflicient operation of the atmospheric evaporator.

In a preferred form of construction, the compressor is driven by a windmill.

One or more intermediate heat-accumulators may be provided, which receive heat from the working fluid on its way from the high temperature heat-accumulator to the low-temperature heat-accumulating device.

The working fluid will reach the condenser tank in the form of wet steam and condensation will be effected by mixing with the water in the tank.

Air from the atmosphere which has been cooled by the atmospheric evaporator may be used for space-cooling purposes in a building, for instance by passing it through a system of ventilating ducts.

The high-temperature and low-temperature intermediate heat-accumulators may take several forms as will be presently described.

The characteristics of the compressor, and of the auxiliary exhausing means that may be employed for assisting the compressor to maintain a vacuum in the evaporator, will be so chosen that a sufiiciently high vacuum is maintained to ensure eflicient evaporation at average atmospheric temperatures, and, at least in a domestic installation, that the vapour at the compressor outlet is superheated by the work done on it to a temperature of at least 225 C. The temperature of the high-temperature heat-accumulator will then be suflicient for cooking and the like purposes.

A typical domestic installation embodying the invention is illustrated by way of example in the accompanying drawings, of which,

Figure l is a schematic sectional elevation of a building showing the components and pipe-runs of the heat pump installation diagrammatically;

Figures 2 to 7 illustrate constructional arrangements of the installation in a somewhat more realistic manner,

Figure 2 being a partial sectional elevation of the building and the components of the installation contained in it and in the ground beneath it.

Figure 3 being a sectional elevation of the top of a windmill-supporting mast embodying an evaporator,

Figure 4 being a sectional elevation taken on the line 4-4 of Figure 3,

Figure 5 being a sectional elevation of the compressor,

Figure 6 being a plan section along the line 6-6 of Figure 5, and Figure 7 being a sectional elevation of a pump for withdrawing condensate and air from the system;

Figure 8 is a heat-flow diagram.

Referring to Figure 1 of the drawings, the heat-pump installation comprises an atmospheric evaporator 10, a compressor 11, a high-temperature heat-accumulator 12, an intermediate heat-accumulator 13 and a low-temperature heat-accumulating device comprising a large tank 14 buried in the soil 15 below the building 16 and containing a body of water 17. A pump 18 in the roof of tank 14 serves for withdrawing excess water and entrained air from the tank and discharging it via a pipe 19 and/or maintaining a predetermined sub-atmospheric pressure in tank 14. Porous pipes 20 closed at each end are disposed in the soil around the tank 14.

The suction side of the compressor 11 is connected with the evaporator 10, the connection being here shown for convenience as a pipe 23 (but see Figures 2 and 5 and description thereof). The suction side of the compressor is also connected by a pipe 24 containing a stop-cock 22 with a ring main 21, to which are connected pipes 21a disposed coaxially within the porous pipes 21 with annular clearance. The pipes 21a are sealed into the'pipes 21 where they enter them at the top and their lower ends are open. A pipe 25 connected to the compressor outlet receives vapour discharged therefrom and passesvia the heat-accumulators 12 and 13, with which it is in non mixing heat-exchange relation, through a pressure regulating valve or restrictor 26 into the tank 14. A pipe 27 connecting the lower end of the evaporator 10 with the lower part of tank 14 drains unevaporated water, which collects at the bottom of the evaporator, into tank 14. Owing to the pressure difference between the vapour space above the water in tank 14 and the interior of the evaporator 10, the water level rises in pipe 27, and the evaporator must be placed high enough above the tank for this column of water not to reach the evaporator. If the required difference of level cannot be provided for, an extraction pump must be provided for removing unevaporated water from the evaporator and the pipe 27 may be dispensed with. The installation also includes a feed-water tank 28 open to atmosphere from which the evaporator 10 is fed, by means hereinafter described. Tank 28 is replenished by means of a pipe 29 from a well 30. To raise water from the well up to the feed-water tank the installation illustrated employs an injector 31 of conventional form fed with water mixed with air at superatmospheric pressure through pipe 19 by pump 18.

The compressor 11, which is shown out of place in Figure 1 to make the figure more legible, is driven by a windmill 32. The driving connection between the windmill and the compressor is illustrated in Figures 2 and and will be described below. The evaporator is constituted by a tubular mast on which the windmill is mounted and which is itself rotatably mounted on top of the building 16, so that the windmill can set itself automatically to the wind as hereinafter described. The mast comprises an inner tube 33 sealed at both ends and constituting the evaporator chamber, which communicates through connection 23 with the suction side of compressor 10, and an outer tube 34 between which and the inner tube is an annular space through which air cir-' culates, as indicated by arrows 35, 35a, 35b, being admitted by a wind-facing opening at the top of the mast and discharged at the bottom of the mast (see'also Figures 2 and 3). Means hereinafter described are provided for discharging the air, cooled by evaporation of the water in tube 33, either outside the building (arrow 35a) or inside it (arrow 35b) for space-cooling in hot weather. A pipe 36, containing a stop-cock or flow regulating valve 37 and having an open lower end, extends downwards into the feed-water tank 28 and upwards within tube 33 nearly to the top of the tube where it terminates in a spraying nozzle or the like. Water is forced up this tube by atmospheric pressure, owing to the vacuum maintained in the tube 33 by the suction of the compressor. Water sprayed into the top of tube 33 from'the pipe 36 trickles down the walls of the tube and is evaporated owing to the low pressure in the tube, the heat of evaporation being abstracted from the air circulating between the tubes 33 and 34. The tube 33 may be lined on the inside with water absorbent material to retain the water and assist evaporation. Heat transfer from the air to the tube 33 is assisted by providing the latter tube with finning 57 which can also cause the air to pursue a tortuous path as it descends the annular space between the tubes.

The high-temperature heat-accumulator 12 is constituted by a sealed tank 38 containing a molten salt-bath, such as a mixture of NaNO and KNO the tank being lagged with a vacuum jacket 39 containing aluminium foil anti-radiation sheets (not illustrated). An immersion coil 25a in the run of pipe 25 is in heat-exchange relation with the salt bath.

The intermediate heat-accumulator 13 is constituted by a hot-water tank 40 in heat-exchange relation with an 1 pipe 42.

Alternatively the tank 40 may be pressurised, if desired, to afford heat at more than 100 C. for pressure cooking or the like purposes. In this case, to prevent back flow through pipe 41, conventional means are provided such as a shut off valve (not shown) to interrupt the feed during pressurizing, or a booster pump (not shown) in pipe 41 operating against the pressure. The pressure and temperature in tank 40 may be maintained at any desired values, say 21 p. s. i. absolute and 110 C.,

by ordinary relief valving.

Space-heating radiators 43 are fed with low-pressure steam through pipes 44 and regulating valves 45 from the vapour space of tank 14.

Below the floor of the building is a thick layer 46 of heat-insulating material, which is kept dry by being laid on a concrete raft 47.

The system also includes a low-pressure steam turbine 48,.here shown as driving an electric generator 49. The turbine is supplied with steam from the outlet of the compressor 11 by a pipe 50, branched from pipe 25 and containing a stop-cock or regulating valve 51, and exhausts through a pipe 52 into the pipe 24 connected to the suction side of the compressor 11.

The installation as illustrated also includes refrigerating means comprising a cold chamber 53 cooled by heatexchange with a tank 54, containing brine or a like low freezing-point substance, the vapour space of which tank is connectible by means of a pipe 55 and stop-cock 56 with the pipe 24 which is connected to the suction side of the compressor 11 The system may further include a pipe 106 extending from a two-way cock 107 in the part of pipe 25 between the heating coil 25b and the valve 26, to the ring main 21. The purpose of this addition to the system is hereinafter explained.

Referring now to Figures 2, 3 and 4, the windmill 32 is mounted on a shaft 58 rotatably supported in a housing 59 and carrying a crown-wheel 60 meshing with a pinion '61 mounted on a crankshaft 63 supported in a bearing bracket 62 secured to the housing 59. The crankshaft 63 articulates with links 64 constituting a connecting rod, in turn articulated on a vertical rod 65 coaxial with tube 33 and entering the latter tube through a gland 66.

The housing 59 is secured to the upper ends of the mast tubes 33, 34, whose lower ends are rotatably supported in bearings 67, 69 respectively (see also Figure 5), the bearing 67 of the outer tube 34 being mounted in the roof of the building. The bearing 69 of the inner tube 33 is mountedon an internal structural member consisting of a thick concrete slab 68 (Figure 5). The lower end of tube 33 is open and is sealed against leakage through the bearing 69 by an annular seal 70 (see Figure 5).

The whole mast comprising the inner and outer tubes 33, 34 and the housing 59 can rotate freely about its axis, and the windmill is offset from the axis of the mast which is situated on the wind-facing side of the windmill, as shown in Figure 3, in which arrows indicate the wind direction. The windmill itself therefore acts as a weathervane for orientating the mast so as to set the windmill to the wind.

The feed-water tank 28 (Figure 2) is in the form of an annular trough surrounding the lower end of tube 33 and has a cover in which is a central opening accommodating the lower end of tube 34 with easy clearance. The air space above the water in tank 28 receives the air circulated-through thersp ace between tubes 33 and 34 from a wind-facing opening 102 in the upper end of tube 34 (Figure 3). Air entering the air space of tank 28 is exhausted either externally through a stack 71 or into the living quarters of the building through a system of ducts, such as 72, the air-flow being controllable by butterfly valves 73, 74. A baflle 75 protects the contents of the feed-water tank 28 against contamination by airborne foreign matter.

The lower end of pipe 36, which is disposed inside tube 33, is brought out through the wall of the tube 33 into which it is permanently sealed and is cranked, as shown in Figures 2 and 5, to dip into the annular troughshaped tank 28, the lower extremity of pipe 36, submerged in the water contained in tank 28, being open. As the mast is orientated by the windmill the external cranked part of pipe 36 rotates with the mast, without meeting any obstruction, owing to the annular form of tank 28.

Referring now to Figures and 6, the compressor 11 comprises a vertical cylinder 76 secured by tie-rods 77 to the underside of the concrete slab 68 coaxially with tube 33 and rod 65 to the lower end of which is secured a piston 78 which slides in the cylinder 76. A sleeve 79, coaxial with and defining an annular space around rod 65, extends from the interior of tube 33 through an opening in slab 68 and a gland 80 in the head of cylinder 76 into the cylinder. Openings 81 in the upper end of sleeve 79 provide communication between the interior of tube 33 and the annular space within the sleeve 79, the lower end of which is open and seatable on the piston 78. The latter has openings 103, within the diameter of the seating of sleeve 79, through which openings pass bars 82 secured to sleeve 79 and carrying a valve disc 83 seatable on the underside of piston 78, the openings 103 being also within the diameter of the seating of disc 83. The disc 83 is spaced from the lower end of sleeve 79 by a distance exceeding the thickness of piston 78.

The slab 68 makes a good seal on the lower race of bearing 69 and on the head of cylinder 76, and the opening in the slab, through which the sleeve 79 passes communicates only with the interior of tube 33. This opening has an enlargement within the slab which communicates with a duct 24a in the slab forming the extremity of pipe 24 (see Figure 2).

At the upper and lower ends of the cylinder 76 are nonreturn outlet valves, here shown as simple gate valves, 84, 85, respectively, which communicate with an outlet manifold 86 to which the pipe 25 is connected.

The arrangement of the sleeve 79 and disc 83 constitutes a double-acting inlet valve to the cylinder admitting vapour from tube 33, via sleeve 79 alternately above and below the piston '78 as the latter descends and rises respectively, as indicated by arrows 104, 105, owing partly to the friction of the sleeve 79 in gland 80 which causes the sleeve to lag behind the piston both in ascent and descent.

Secured to the underside of disc 83 coaxially with rod 65 is a rod 87, which extends through'a gland 88 in the base of cylinder 76 to operate the pump 18 (see Figure 2). Referring now to Figure 7, pump 18 comprises a vertical cylinder 89 mounted in the roof 14a of tank 14 and containing a piston 90, pierced by openings 91 which can be closed from below by a valve disc 92 secured to the end of rod 87 which passes through the piston 90 with sliding fit. A shoulder 93 on rod 87 limits relative axial movement of the piston 90 on rod 87 in the direction away from disc 92. In the head of the cylinder 89 is a non-return outlet valve, here indicated by a simple gate valve 94, communicating with an outlet cavity 95 having an opening (not shown) communicating with pipe 19 formed in a capping member 96 secured in fluidtight manner to the tank roof 14a and incorporating a gland 97 through which the rod 87 passes. Cavity 95 is sealedfrom the interior of the tank 14 in any convement way. It will be evident that pump 18 operates 1n the manner of an ordinary lift pump with a non-return valve on the delivery side.

Referring once more to Figure 2, the vacuum lagging of the high-temperature heat-accumulator 12 is continued below the base of the tank 38 to form a cavity. An oven 98 supported on a pillar 99 can be raised into this cavity into contact with the base of tank 38 by means of a rack and pinion gear enclosed in a housing 100 and operated by a hand crank 101. The oven is shown in full lines in the raised position and in dotted lines in the lowered position, in which it can be loaded and unloaded.

The normal cycle of the installation is as follows:

As long as the windmill 32 is working the compressor 11 applies suction to the evaporator 10 and lowers the pressure therein. Water sprayed into the evaporator tube 33 from pipe 36 is evaporated at this reduced pressure, the latent heat of evaporation being extracted mainly from the air flowing over the outside of tube 33 through the outer tube 34, i. e. from the atmosphere. This airflow is maintained by the wind. Heat will also be extracted from the Water itself, but will be replaced by conduction through the wall of tube 33 as soon as the temperature of the water inside the tube falls below the temperature of the air outside it. If the sun is shining brightly, solar radiation falling on tube 34 will be absorbed and conducted from the inner wall of the tube, and some of its heat-equivalent will be transmitted to the interior of the tube 33 along with the heat extracted from that originally present in the atmosphere.

Water vapour sucked into the compressor 11 is compressed therein and thereby superheated.

This superheated vapour passes through the immersion coil 25a of the high-temperature heat-accumulator 12, to which it yields some of its superheat, and thence to the heating-coil 25b of the intermediate heat-accumulator 13, to which it gives up the greater part of the remaining superheat. densed, the latent heat of condensation being taken up by the water in that tank. Excess condensate is returned to atmospheric pressure acting on the water in the feed tank 28 to reach the top of pipe 36 water is sprayed into the evaporator tube 33 from the top of pipe 36 and will trickle down the inside of the tube and evaporate.

For the cycle to have a good volumetric performance, air must be substantially excluded from the system although the presence of some air is not otherwise detrimental and may even be beneficial if the evaporation temperature is very low.

When the system has reached a stable condition, the suction pressure will be approximate to and cannot fall below the vapour pressure of the working fluid (water) at the temperature of evaporation, provided air-leaks are substantially excluded. Similarly, the delivery pressure cannot fall below the vapour-pressure over the liquid in the tank 14, which receives the condensate, depending on the temperature of the contents of the tank. In general, it must be slightly higher on account of loss of head along the run of pipe 25, depending mainly on the heatexchange characteristics of the heat-accumulators 12 and 13, but it may be artificially raised above the pressure in tank 14 by means of the valve or restrictor 26, which may be arranged to impose a minimum back-pressure on the compressor delivery, so selected that with the highest evaporation temperature encountered the temperature of the vapour delivered by the compressor will be high enough, allowing for heat-exchange temperature drop, to

It then passes into tank 14, where it is con raise the high-temperature heat-accumulator 12 to a temperature adequate to the services demanded of it.

In the example illustrated heat for cooking is obtained from heat-accumulator 12, which must therefore have a temperature of at least 225 C. and preferably nearer 250 C.

The volumetric compression ratio of the compressor must be adequate to'enable it to deliver against the highest back-pressure encountered when working with the lowest evaporation temperature encountered.

To ensure that air is substantially excluded from the vapour-space above the water in tank 14, the pump 18 must be capable of maintaining suction on this space down to the value of the vapour pressure over the water in the tank corresponding to the minimum temperature normally occurring in the tank, estimated at about 55 C., for which the vapour pressureof water is about 2.3 lbs/in? absolute.

It is intended that the atmospheric evaporator will be used during the warmer months of the year, during which heat will be accumulated in the tank 14 and the surrounding soil 15. In the colder months heat-leakage from tank 14 through the surrounding soil will be utilised for evaporation by means of the soil-pipes 20. Under average British conditions, a mean evaporation temperature of about 15 C. may therefore be assumed for the atmospheric evaporator 10, and for the soil-pipes 20 it is estimated that the temperature of the surrounding soil will have reached about the same or a slightly greater value by the end of October and will thereafter progressively fall to about C., or less, at the end of March. The cycle when using the soil-pipes as evaporator is therefore similar to that when using the atmospheric evaporator.

The highest temperature to be expected in tank 14 is estimated at about 95 C. for which the vapour pressure is just sub-atmospheric, and the compressor must be capable of delivering against such a pressure when evaporation is taking place at the lowest temperature normally utilised, say 10 C.

The following data represent the maximum operating ranges contemplated for the system:

The pressure at compression will exceed condensation pressure only enough to offset frictional losses through the pipes. The values for evaporation apply to both atmospheric evaporator 10 and soil evaporators 21a while the values for condensation apply to both tank 14 and space heaters 43 which are, in effect, an extension of tank 14.

For a normal cycle, evaporation will take place at about 17 C. under a pressure of 0.28 p. s. i. a., condensation at about 75 C. under a pressure of 5.7 p. s. i. a., and the compression ratio will be 201 with the temperature of the superheated vapor at the compressor outlet at about 300 C. Under these conditions the mean temperature of the vapor in coil 25a will be about 250 C., the vapor in coil 25b roughly about 125 C., and the vapor-liquid equilibrium mixture in space heaters about 75 C.

It will be understood that the compression ratio adjusts itself automatically through the operating range, as a result of the use of automatic valving in the compressor, dependent under the vapor pressures of water at evaporation and condensation.

In certain circumstances it may be desirable to transfer heat to the soil directly rather than by leakage from the tank 14. In such circumstances the cock 107 can be thrown over so that the vapour after traversing coil 25b flows, via pipe 106 and ring main 21, by-passing the tank 14, to the porous pipes 20, which then act as condensers, the heat 'of condensation being transferred directly to the soil 15. Extraction of the condensate from pipes 20 is eflfected'by intermittently throwing over cock 107 and opening cock 22 to'connect the ring main 21 and pipes 21a to the suction of the compressor 11, which will then pump the condensate back through the system into tank 14.

Since the latent heat o'fsteam varies by less than 10% between the temperature of evaporation (0 C. to 15 C.) and that of condensation C.), the superheat of the vapour extracted mainly by the high-temperature and intermediate heat-accumulators 12, 13, is substantially equivalent to the mechanical energy expended on it by the compressor. It has been estimated that the demand for high-temperature heat in the installation illustrated will coincide approximately with the total amount of superheat. generated.

The heat-flow diagram (Figure 8) illustrates the operation of the installation over a complete year. The ordinates represent heat units on an arbitrary scale and the abscissae represent time, the time scale being divided into twelve intervals of one calendar month each starting with April and ending with March, and designated Ap, My, J, Jy, A, S, O, N, D, Ia, F, M. The intercepts of the ordinates by the boundaries of the shaded areas represent the total heat units accumulated or/ and utilised or/ and wasted from the zero epoch a to the epoch of the ordinate in question. Intercepts of the shaded area below the axis of abscissae ax represent heat units transmitted to the soil surrounding the tank 14 (Figure l) and subsequently recovered in part. Heat received by the atmospheric evaporator from April to October, inclusive, is represented .by the shaded area between the lines ab and ac, the intercepts of the ordinates by these lines representing the total heat units so received at any date. A substantially equal amount of heat, appearing as latent heat of condensation, is trasferred to the water 17 in tank 14. The total heat units so transferred by the end of October is represented by the bracket I. Part of this heat is accumulated in tank 14 and part, represented by the bracket II, has leaked into the surrounding soil 15 (Figure 1). The heat equivalent of the mechanical work performed by the compressor is represented by the shaded area between the lines ace and adj, the intercepts of the ordinates by these lines representing the total heat units so produced at any date. This heat appears as superheat and is taken up by the high-temperature and intermediate heat-accumulators 12, 13. The total heat intake of these accumulators is represented by the bracket III. It is substantially balanced by current consumption of highand intermediatetemperature heat, the total of which is indicated by the arrowhead g. Of the total heat-leakage to the soil (bracket II) part represented by arrowhead h is permanently lost, the remainder, represented by the bracket IV, being recovered during the months November to March inclusive. During this period the soil-pipes 20 (Figure 1) are connected to the suction side of the compressor and serve as the evaporator of the system, abstracting the heat represented by bracket IV from the soil; and the heat of evaporation is re-cycled through the system andreturned to the water 17 in tank 14 (Figure l). The cumulative heat-units so recovered and recycled at the end of each month are represented by the intercepts of the ordinates between the lines bi and bi. The total quantity of utilisable heat transferred to the tank 14 is represented by the intercept ek and over the whole period, April to March, inclusive (or ak), this is substantially balanced by current consumption for space-heating, mainly confined to the winter months November-March, indicated by arrowhead I.

We claim:

1. A heating system for supplying the requirement of heat for domestic and like purposes, such as that re quired for space-heating and the like, in which such heat is derived from the atmosphere, said system embodying a single working fluid circuit employing water and its vapor as the working medium and operating on an evaporating and condensing cycle at sub-atmospheric pressure: the system comprising an atmospheric evaporator; means supplying water to said evaporator wherein the water is vaporized; a compressor having an inlet and an outlet; a conduit connecting said atmospheric evaporator with said inlet; flow control means in said conduit operable to provide flow of vapor therethrough to said inlet, whereby the compressor may draw vapor from the atmospheric evaporator at a sub-atmospheric pressure and apply heat thereto by increasing the pressure; motor means for driving said compressor; condenser means comprising heat accumulating means; means conducting the working fluid from said compressor to said condenser means; said heat accumulating means comprising a rela tively large tank buried in the ground and containing water in heat-exchange relationship with water condensed from said system; heat-exchange means for extracting heat from said tank for space heating and like purposes; said tank being in heat exchange relationship with the surrounding soil, said surrounding soil constituting an accumulator of heat at low temperature, means also buried in the soil surrounding and spaced from said tank for extracting and vaporizing moisture normally contained in the body of soil between said tank and said last named surrounding means; a conduit connecting said last named means with the inlet of said compressor, flow controlling means in said conduit operable alternatively with said first named flow controlling means for operatively connecting said last named extracting and vaporizing means with the suction inlet of said compressor, whereby when the atmosphere is at a higher temperature than the said last-named extracting and vaporizing means, the atmospheric evaporator may be connected to the compressor to apply heat to the working fluid, the heat not utilized by said heat-exchange means being stored in said tank and said body of soil, and when the atmosphere is at a lower temperature than said soil-immersed evaporator, the latter may be placed in communication with the compressor to supply heat to the vapor extracted from the pre-heated soil moisture.

2. The system as set forth in claim 1 in which a windmill is operatively connected to said compressor and employed as the motor means for operating said compressor, and in which the heat accumulating and storing means comprising the buried tank and the surrounding body of soil is of great heat storage capacity thereby permitting the efiective utilization of wind power even though variable and intermittent.

3. The system as set forth in claim 1 in which the buried extractor and vaporizing means comprises pipes made of finely porous material adapted to receive water from the moisture in the surrounding body of soil by percolation, and capable of maintaining in their interiors sub-atmospheric pressure of generally the same low value as is required for the atmospheric evaporator, and in which there is provided an insulating and substantially moisture-impervious layer above soil-immersed condenser and evaporator means, which latter means comprises the tank, the surrounding extractor-evaporators, and the in tervening body of soil.

4. The system as set forth in claim 1 in which the working fluid is water and its vapor, and including means for feeding Water to the atmospheric evaporator at a very low sub-atmospheric pressure, said last named means including a feed water tank open to atmosphere and a stand pipe whose lower end is submerged in said feedwater tank and whose upper end communicates with the interior of said evaporator; said stand pipe being high enough for the water to reach its upper end, under the atmospheric pressure to which the feed water tank is subjected, only when the pressure in the atmospheric evaporator is decreased to the required low-sub-atmospheric value; said apparatus further including pump means communicating with said condenser and driven by the compressor-motor means for maintaining sub-atmospheric pressure in said condenser, such pressure being higher than that in the atmospheric evaporator, and for discharging excess condensate from the condenser against atmospheric pressure.

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